The invention concerns a rheometer having a measuring shaft which is borne for rotation about and/or axial displacement along its longitudinal axis and with a measuring device for measuring the normal forces and/or the torque which acts on the measuring shaft during the measurement.
The measuring of rheological quantities of a material using a rheometer is based on the precise knowledge of the relationship between the tensile forces and the deformation of the material. In order to extract the material properties from these characteristic dependencies it is necessary to measure the tensile force and the deformation of a material sample in as precise a manner as possible. The sample is disposed between two plate-shaped measurement components, with one of the measuring components being connected to a driven measuring shaft by means of which a shearing force can be introduced onto the sample. During the measurement, an additional normal force acts on the measuring shaft as well as a resulting torque about the axis of the measurement shaft, both of which depend on the material in the sample and are measured and utilized to determine the material characteristics.
In former times, it was customary to bear the measuring shaft on an apparatus housing using springs and to determine the deformation of the springs during the course of the measurement. The deformation of the springs, together with the knowledge of the stiffness of the spring and/or of the spring constant were used to determine the normal forces and the resulting torques. In more modern rheometers, the displacement of the measuring shaft is determined either using optical procedures while taking advantage of the refraction of light in a narrow gap or by making use of electro-capacitive techniques. Both procedures are difficult from a technical point of view and, in particular with respect to the optical procedures, are limited with respect to their precision.
It is the underlying purpose of the invention to introduce a rheometer of the above mentioned kind with which the normal forces and/or the torques on the measuring shaft can be determined in a straightforward fashion.